Known injection devices are shown in WO 95/35126 and EP-A-0 516 473 and tend to employ a drive spring and some form of release mechanism that releases the syringe from the influence of the drive spring once its contents are supposed to have been discharged, to allow it to be retracted by a return spring.
It is known to provide a safety interlock around the needle of such injection devices.
Such a safety interlock prevents accidental activation of a trigger of the injection device by preventing rotation of the trigger. The interlock is sprung loaded out of the aperture through which the syringe extends once activated. The interlock is disengaged by pressing it in towards the aperture by, for example, pressing it against a user's body, thereby allowing the trigger to be activated and the syringe to be extended.
The interlock has to be biased out of the aperture so that it can be activated. Known devices use small coil springs positioned between the housing of the injection device and the interlock. These small springs are costly to assemble and introduce a risk that they may be missed out all together during the manufacturing process.